If your only sticking point is the drawer runners and you are time short, just chuck whatever is supplied with the kit and upgrade to Blum Metabox drawers. They are pretty much the top of the line drawer runner, and are available in standard or full extension flavours.
From memory they are about $25-30 per drawer (Bunnies price, you could do better through a proper kitchen supplies place if buying a kitchenload), don't require any fancy box making skills (drawer bottom and drawer back need to be supplied by you, but this is just standard 16mm melamine faced board cut to size with a bit of iron on edging for the top of the back piece).
http://www.blum.com.au
Hettich make something similar - the MultiTech. I haven't used them, but I would expect that they are pretty much comparable.
So if you were ordering a kit, rather than ordering the 450 wide drawer cabinet, you'd just order the 450 wide cupboard (or whatever size you were after) and nip off to the local hardware store to get the bottoms/backs cut if you don't have a circular saw handy.